Q.Why does molarity of a solution depend upon temperature ?

Reasoning. Molarity $M = \dfrac{\text{moles of solute}}{\text{volume of solution in litres}}$. The number of moles of solute in a given solution does not change with temperature, but the VOLUME that solution occupies does change slightly with temperature (most liquids expand on heating and contract on cooling).

Consequence. Since the denominator (volume) changes with temperature while the numerator (moles of solute) stays fixed, the calculated molarity value itself changes with temperature, even though nothing about the amount of dissolved substance has actually changed. …

Trace through the molarity formula and identify which term (volum …

• Believing the moles of solute change with temperature (they do not — only the solution's volume does). …